I have a Thomas in my 10'x10' darkroom. It is in the middle, close the 8' ceiling.

I replaced the filter in the upper gates with a piece of cardboard painted flat black. The yellow filters are in the unit near the light. When I print silver gelatin, the gates are open about 1-1 1/2". When working with alt processes the gates are wide open.

I have used them in this manner for about 20 years and never had a fogging problem.